Uh, farp, you may want to check your units. 379 micrometers equates to 0.379 millimeter, or 0.015 inch. A typical piece of 24 weight office paper is about 0.005 inch thick. So, your kayak hull is only about three sheets of paper thick!
Your numbers sound somewhat reasonable if you meant to say thousandths of an inch.
I did find one manufacturer who specs their aluminum canoes with a hull thickness ranging from 0.030 to 0.050 inch. Of course, marv, if you are wondering about a whitewater kayak, the numbers should be quite a bit larger. Farp's numbers (0.397 to 0.600 inch) sound somewhat reasonable (probably a bit thick), so long as you read micrometers as thousandths of an inch! As a visual guess, my Blitz Special is about 3/16, or 0.1875, inch thick at a far aft point on the stern deck. I found that out by installing an aftermarket drain hole and plug (had to drill a hole). I would expect the hull to be thicker, but probably not by too much. Hmm...upon further thought, I think farv was just trying to be funny and made up some numbers. Realistically, I think his low end number (about 3/8 inch) is more likely a maximum hull thickness. Much more than that and you would never see the hull flex like it does. It's likely that we'd need some means of transport other than our shoulders for our boats, too (more material -> heavier boat).
Marv, I think you ought to take my thoughts here with a grain of salt. I have never actully designed or built a kayak. Heck, I haven't even broken out the calipers to make an acurate measuement of hull thickness. I'm just a lowly Physics and Engineering junior with an eye for practicallity and a tendancy to over design.